(1) Field of the Invention
The present invention relates to a silicon field emission emitter and method for manufacturing the same. The silicon field emission emitter may be utilized as an electron sources in various displays, light source, amplifying devices, high speed switching devices, a microsensor and so on.
(2) Description of the Prior Art
Recently, attention is concentrated on an inefficient thermionic emitter that is substituted for a high field emission emitter. The emitter is very efficient since an emitter material does not need to be heated. The emitter has been used for scanning sources of an electron microscope for several years, and the emitter is now being developed as a source for a vacuum microelectron device, a flat panel display, and a high efficiency and frequency vacuum tube.
The field emission emitter may have very high luminous efficiency and luminescence by making a point of the field emission material of which a radius is less than about 100 nanometers high-integrated to 10.sup.4 -10.sup.5 Tips/mm.sup.2, and thus is thought as a very suitable display device for the embodiment of wall television sets owing to a low voltage consumption.
Besides, even though silicon has a low melting point and electric conductivity, the applicability is gradually increased by the variety of the microfabrication technology that can facilitate fabrication of sharp emitter tips by means of silicon.
FIG. 1 illustrates a preferred embodiment of a typical structure of the silicon field emission emitter. A reference numeral, 11 indicates a silicon substrate doped with impurities of high density and having high conductivity. Also, a cone-shaped emitter 17 is formed within a cavity 15 in an insulating layer 13 on the silicon substrate 11. And a gate electrode 19 made of a molybdenum thin film is deposited on an insulting layer 13.
FIG. 2 shows a perspective view of a prior art display using the field emission emitter as the electron sources ( Refer to Japan Patent Unexamined Publication Sho 61-221783).
Referring to FIG. 2, an emitter electrode 21 doped with impurities of high density is formed on the silicon substrate 20 in accordance with the directions of columns 22, and a cone-shaped field emission emitter 26 and an insulting layer 23 is formed on the emitter electrode 21. Also, a plurality of gate electrodes 25 is formed on the insulting layer 23 in accordance with the directions of rows 24. Cavities or holes 15 are formed at the opposite side of the cone-shaped field emission emitter 26 of the gate electrode 25.
Meantime, on an upper substrate 27, a transparent conductive layer 29 and a fluorescent layer 28 are respectively deposited to be fixed to the upper substrate 27 in a beta configuration. The lower substrate 20 and the upper substrate 27 together with a spacer (not shown) form an outside of a vacuum tube.
The operation of the above-mentioned display is as follows:
Positive electric potential is applied to the transparent conductive layer 29. Responsive to a display signal, predetermined electric potential difference is given between the emitter electrode 21 in the columns 22 and the gate electrode 25 in the rows 24. An appropriate electric field is formed between the gate electrode 25 and the cone-shaped field emission emitter 26, such that electrons are emitted from a cone-shaped tip. The electron is emitted from the cavity 15 of the gate electrode 25 to the fluorescent layer 28, then the fluorescent layer 28 radiates.
For example, by biasing the gate electrodes 25 within the range of several tens voltages to several hundreds voltages to the substrate 20, the electronic field is generated between the cone-shaped microtip emitters 26 and the gate electrodes 25, and emission current of about several mA is obtained from the tip of the emitters 26.
An image in accordance with the display signal is displayed by the above-mentioned operation.
The prior art silicon field emission emitters have some disadvantages in forming the insulating layer 13 and the gate electrode 19. Since the insulating layer 13 is generally formed by inclination deposition using an electron beam evaporator, the characteristic of the insulating layer is bad and a breakdown voltage value of the deposited film is less than 4 MV/cm. Accordingly, there are disadvantages that the thickness of the insulating layer should be limited to more than one micrometers, a making process is complicated and it takes longer to make the emitter to keep a safe breakdown voltage value by a high field formed between upper and lower electrodes. In addition, another disadvantage is that it takes longer for the emitter and applied voltage to become higher because the diameter of the cavity 15 becomes wider in forming the gate electrode by inclination deposition using an electron beam evaporator.